The Anglo-Saxons were a group of Germanic peoples who inhabited the regions now comprising the Netherlands, northern Germany, and southern Denmark. They began to migrate to Britain in what scholars believe was about the fifth century CE, and were mostly Christianized by the end of the sevent century. They formed a number of loose chiefdoms which eventually gave rise to more solidified kingdoms, including Northumberland, Mercia, Kent, East Anglia, Wessex, Sussex, and Essex, along with several others.
Power and political relations between these kingdoms was fluid, but by the late ninth century, Wessex, which was ruled by Alfred the Great, became by far the most powerful, and Alfred was acknowledged as a ruler by many of the kingdoms in the south, largely due to his success in fending off the relentless Viking invasions that plagued the island throughout his reign.
Alfred's successors ruled over an entity that has been recognized by scholars as essentially an English kingdom. Eventually, Scandinavian invasions resumed. One, Harald Hardrada, invaded to press his claim to the throne, in 1066, and while Harold, the Anglo-Saxon king, was able to defeat his army at the battle of Stamford Bridge, he was unable to drive off the Norman invaders that landed on the south shore of the island shortly thereafter. Harold was killed, and William's accession to the throne ended Anglo-Saxon control of the English monarchy.